Preheat your oven to 350°F (175°C). Gather all required ingredients for preparation.

In a large pot of salted boiling water, cook the lasagna noodles until they are al dente, following package instructions. Drain and set aside.

In a skillet over medium-high heat, warm the olive oil. Sauté the chopped mushrooms, onions, and minced garlic until the onions become tender. Remove any excess liquid and let the mixture cool.

Simultaneously, boil a small pot of water and cook the fresh spinach for about 5 minutes. Drain thoroughly, allow it to cool slightly, and squeeze out any remaining liquid before finely chopping.

In a mixing bowl, blend the ricotta cheese, Romano cheese, egg, salt, oregano, basil, and black pepper until smooth. Incorporate the sautéed mushroom mixture and the prepared spinach, mixing until evenly combined.

In a 9x13-inch baking dish, arrange 5 lasagna noodles to form the base layer. Spread one-third of the ricotta-spinach mixture over the noodles. Sprinkle 1 cup of mozzarella cheese and ⅓ cup of Parmesan cheese over the mixture. Top with 1 cup of tomato pasta sauce, spreading it evenly.

Repeat this layering process two more times, using the remaining ingredients. Cover the dish tightly with aluminum foil to retain moisture while baking.

Bake the lasagna in the preheated oven for 1 hour. Once baked, allow the dish to cool for 15 minutes before serving to let the layers set.

This spinach lasagna delivers a harmonious combination of textures and flavors, making it an ideal choice for a satisfying meal.